1. Field of the Invention
The present invention relates to an anchoring device for affixing a surgical suture to a bone and an installation tool for deploying same.
2. Description of the Related Art
Various surgical procedures require soft tissue, such as ligaments, tendons, muscles and the like, to be attached to bone. Such surgical procedures include, for example, repairing knee and ankle ligaments, rotator cuff tears, and glenohumeral instability. In certain situations, it is desirable to anchor a suture to a bone and then use the suture to attach the tissue to the bone.
Various devices are known for affixing a surgical suture to a bone. One such device consists of a staple-like structure having at least two leg portions and a body disposed between the legs. This staple-like device is attached to bone by driving the legs into the bone so that a suture can be secured between the bone and the body of the staple. This procedure, however, is often difficult to perform in areas where access to the bone is limited. As a result, it is frequently necessary to place the staple at a less than desirable location. Furthermore, a plurality of bores must be made in the bone in order to secure the suture thereto, which has obvious disadvantages.
Another suture anchor, taught by U.S. Pat. No. 5,141,520, consists a cylindrical body and a solid conical-shaped harpoon-type head attached to the body. A suture is attached to this harpoon-type anchor by securing one of its ends within the anchor body with the other end extending from the rear thereof. The solid conical-shaped head enables the anchor to be driven into bone without first drilling a bore. Once in the bone, a flexible skirt around the base of the conical-shaped head acts as a barb to hold the anchor in place.
It can be difficult to achieve a proper level of flexibility in the skirt to enable the skirt to spread away from the anchor widely enough to engage a relatively large portion of the interior surface of the bone and yet be flexible enough to enable the anchor to be driven into the bone without excessive resistance. Furthermore, because only one end of the suture extends from the bone, two such harpoon suture anchor devices must be driven into the patient's bone if two suture ends are needed to attach the tissue to the bone. This has obvious disadvantages. Also, it is impossible to substitute one suture for another in a given anchor because the suture is fixedly secured within the body of the anchor. To use different sutures during a given surgical procedure, the surgeon must have a number of pre-loaded suture anchors at his disposal. Furthermore, there is the possibility for the end of the suture to detach from body, due to the difficulties inherent in affixing one end of a suture into a solid object.
The harpoon-type suture anchor is driven into the bone using a hollow driving rod. The anchor is loaded into one end of the rod such that the conical head projects from the rod, with the rear of the anchor, including the suture, disposed within the rod. The anchor is driven into the bone by a hammer force transmitted through the rod. Depending on the strength of the bone, a large amount of force may be required to insert the anchor. Thus, the surgeon must be highly skilled to ensure that the driving force is properly applied to the anchor and that the anchor is not driven too far into the bone. Moreover, the greater the force required to insert the suture anchor, the greater the probability that the rod and/or suture anchor will be damaged. Also, the trauma to the patient's bone and surrounding tissue increases. Because a portion of the anchor is disposed within the driving rod, there is the possibility that the anchor will not properly pull out of the rod once in the bone.
In other types of suture anchor devices the anchor is not driven directly into the bone but instead is placed within a bore formed in the bone. One such device, taught by U.S. Pat. Nos. 4,898,156 and 5,046,513, consists of a metal cylindrical body having at least one flexible tail or barb extending from a rear end thereof. The body and barb are inserted into a bore prepared in the bone. The flexible barb is straightened as the anchor is inserted into the bore and returns to its original curved position to engage the side wall of the bore, once fully inserted, thus preventing the anchor from being pulled out of the bore. In this device, however, the barb may unwantedly penetrate the side wall of the bore due to the fact that the barb has a relatively narrow portion that engages the side wall. Additionally, this type of anchor may be rendered ineffective should the barb: be too flexible; not properly engage the side wall; break; or become detached from the body of the anchor. It is not possible to insert this anchor into a bore so that the rear end of the anchor is flush with the bone surface, because the barb must be fully seated within the bore.
In the type of suture anchor just described, only one end of the suture is attached to the anchor body. Specifically, a knot tied in the suture holds the suture within the anchor body. The free end of the suture extends from the body and out of the bore. This method of attaching the suture to the anchor suffers the same disadvantages discussed above with respect to the harpoon-type suture anchor device wherein only one end of the suture is available to attach tissue to the bone. Also, there is always the possibility that the knot may become undone. Furthermore, if the suture is attached such that it does not extend from the anchor along its longitudinal axis, or if the anchor is not held within the bore such that its longitudinal axis is parallel to the centerline of the bore, tension on the suture will impart a torque on the anchor due the asymmetrical load applied to the anchor. This torque can cause the anchor to twist within the bore resulting in the barb undesirably penetrating the side wall.
One installation tool for deploying the just-described anchor into the bore consists of a tubular body member into which the anchor is loaded tail first so that the barb extends straight from the body into the hollow portion of the installation tool. A plunger slidably disposed within the tubular body forces the anchor into the bore. Because the barb projects beyond the rear of the anchor, the plunger must engage the barb during the insertion procedure. This has a disadvantage in that the flexibility of the barb may not provide a solid surface for the plunger to act upon. Also, there is a possibility that the plunger force acting on the barb may damage the barb or its attachment to the anchor body.
In this type of insertion device, the end of the tubular body within which the anchor is disposed must be placed in the bore so that the anchor can be expelled from the insertion device fully within the bore. Therefore, it is necessary to dimension the bore wide enough to receive the anchor and the surrounding end portion of the insertion device. Consequently, a bore wider than just the anchor is required. The wider bore can allow the anchor to twist undesirably therein, especially when an asymmetrical load is applied on the anchor. Furthermore, skill is required to ensure that the insertion device is not placed too far into the bore and to position the anchor within another bore at the same depth on repeated occasions.
To attach the suture to the anchor while using the installation tool just described, the anchor must be pushed out of the insertion device far enough for the person loading the suture to access the anchor body. Thereafter, the suture must be tied in a knot and loaded into the anchor. This is a relatively complicated and delicate procedure, making changes in the type or size of suture difficult and time consuming.
A second known embodiment for the just described installation tool consists of the above described tubular body and plunger and also incudes a hollow loading member. Instead of loading the anchor into the tubular body, the anchor first is loaded tail first into an end of the loading member so that the body of the anchor around the barb abuts the end of the loading member. The loading member, with the anchor therein, is then inserted into an end of the tubular member opposite that just discussed above. Actuating the loading member positions the anchor outside the insertion device for attaching the suture. The plunger is used to deploy the anchor from the loading member and tubular member as discussed above. While this type of installation device makes it easier to access the anchor for loading the suture, it has three elements, is relatively complicated, and the procedure for using it must be performed carefully so as not to damage the suture anchor. Also, a significant amount of time is required to align the ends of the anchor with the ends of the installation members and to align the ends of the installation tools with one another. As a result, quickly loading a series of anchors in one installation tool is difficult.
As with the previous installation tool, the end of the tubular member must be placed within the bore necessitating the use of bore wider than the anchor. Also, skill is required to ensure that the tubular member is properly placed into the bore and to consistently position the anchor within the bore at the same depth.
A further type of anchor is taught by U.S. Pat. No. 4,946,468 and is structurally similar to the barb-type suture anchor discussed above. In this anchor, the suture is wrapped around a pin in the anchor body so that both ends of the suture extend from the bore. However, each suture end extends from the bore at substantially the same location, which can result in unwanted tangling and knotting of the suture. This barb-type anchor also suffers from many of the disadvantages discussed above with respect to the first-described barb-type anchor. For example, the rear of anchor can not be inserted flush with the bone surface, the barb is susceptible to breaking or malfunctioning, and the anchor may twist within the bore.
The installation tool for inserting this further version of a barb-type anchor includes a handle with a cannula attached thereto. The anchor is fitted into an end of the cannula such that a portion of the anchor remains outside the cannula. A slot in the canula receives the barb so that the barb remains in its unflexed, curved position. A suture is attached to the portion of the anchor remaining outside the cannula. Loading the suture can still be difficult and time consuming, because the suture must be threaded into the anchor body, wrapped around the pin, and then threaded back out of the body.
The anchor is inserted into a bore by pushing the cannula with the loaded anchor into the bore through the actuation of the handle. The anchor is pulled out of the cannula by the engagement of the barb with a side wall of the bore. Using the barb to dislodge the anchor from the insertion device can result, however, in unwanted force on the barb and on the side wall of the bore, especially if the anchor fails to slide easily out of the cannula. On the other hand, if the anchor slides out of the cannula too easily, it can be difficult to keep the anchor in the cannula, especially when loading the suture. As with the previous insertion devices there is no means to ensure that the anchor is inserted to the same depth in repeated procedures. Instead, the surgeon must judge when the anchor is inserted far enough into the bore.